The present invention relates to containers for blood. Containers of this type are currently used, for example, for transfusion purposes and in surgery for receiving and holding quantities of blood taken from the patient's body, for example, when the body is connected in an extracorporeal circulation system.
In general, two kinds of container of this type are known in the art: (1) those constituted by actual bags, envelopes of sheet material suitable for use in contact with blood (for example, PVC or polyurethane), forming generally flexible envelopes which can swell up to a greater or lesser extent according to the quantity of blood with them; and (2) hybrid solutions, such as that described in U.S. Pat. No. 4,424,190, in which the container comprises a concave, rigid, cylindrical shell and a flexible membrane. At rest, the membrane is disposed close to the internal wall of the shell and, when the blood flows into the container, the membrane bulges to a greater or lesser extent and, in the condition in which it is filled to the maximum permitted by the container, reaches a shape approximately complementary and symmetrical to that of the rigid shell.
Whichever solution is used, the container usually has at least one connection for the inlet of blood (taken from the patient's body), a vent for any air trapped in the blood, and at least one outlet. Particularly in applications in an operating environment (extracorporeal circulation systems with blood oxygenators) there is usually also a further connection for the return of blood from the cardiotomy, as well as a connection for recirculation from the oxygenator.
In this latter situation of use in particular, it is imperative to ensure that any air entrained by the blood flowing into the container is eliminated as completely as possible. In fact, any air trapped in the blood may fragment, even at a microscopic level, and this may result in more or less extensive damage to the patient to whom the blood is reinfused. For this reason, it is current practice for a container of the type specified above to have, downstream of the blood inlet connector, a filtering rete or screen (constituted, for example, by a sheet of polyester or polyamide with holes having diameters of the order of 40-200 microns) through which the blood entering the actual holding space of the container is intended to pass. The blood is filtered and the trapped air, which diffuises upwards to be discharged to the exterior through the corresponding vent, is consequently eliminated.
In both of the solutions considered above (a completely flexible bag and a container comprising a rigid shell), the filtering screen is usually also a flexible element which follows the deformable parts of the bag in their bulging and flattening movements resulting from the flow of blood into and out of the container. This solution is unsatisfactory from various points of view. In particular, it encourages the formation of preferred blood-flow directions within the container, resulting in the formation of stagnant regions. Thus, in many cases, as a result of its very flexibility, part of the filtering rete remains in a position close to the flexible wall of the container and adhering thereto when the container swells up, and the adhering portions of the screen thus perform no useful function.